This work reports the results of laboratory experiments conduced to follow the kinetics of stront... more This work reports the results of laboratory experiments conduced to follow the kinetics of strontium recovery into the Al-Mg alloy by metallothermic reduction of SrO. The reagent was incorporated to molten alloy by the use of submerged powders injection technique. The variables analyzed were the injection time, the melt temperature and the initial magnesium content. Magnesium is added to the melt to increase the reactivity and reduce the surface tension of the molten aluminum. It was possible to increase the strontium content from 0 to 5 wt.% after 60 min of treatment. The results were fitted to a general kinetic equation, which allowed it to obtain the kinetic parameters, i.e. order of reaction and activation energy of the process. As the main mechanism of the strontium recovery process is of diffusive type, the global process rate increases as the temperature and initial amount of the magnesium increased.
This work presented the feasibility of cerium recovery by Al-Mg alloy through the metallothermic ... more This work presented the feasibility of cerium recovery by Al-Mg alloy through the metallothermic reduction of CeO 2 to obtain a master alloy Al-4%Ce. The master alloy obtained in this investigation was for the grain refinement and modification of Al-Si alloys. The reagent was incorporated into a molten alloy using the submerged powder injection technique, and metallic samples were obtained during injection. Chemical and microstructural analyses (by inductively coupled plasma (ICP) and scanning electron microscopy (SEM), respectively) confirmed the possibility of Ce uptake in the bath (0 to 4 wt.%), as CeO 2 was reduced through metallothermic reactions in the molten alloys. Based on the characterization of reaction products, the sequence of the reaction was proposed.
Al respecto, Bunt (1988) señala que la calidad de las plántulas depende del tipo de sustrato dond... more Al respecto, Bunt (1988) señala que la calidad de las plántulas depende del tipo de sustrato donde se desarrollan, en particular de sus características físico-químicas, ya que el desarrollo y el funcionamiento de las raíces están MS treatment. The species with the highest germination response was E. dasyacantha (92.6%), followed by A. myriostigma (54.07%). This protocol calls for the convenience of using zeolites as a replacement for agar substrate, thus promoting the cacti in vitro conservation, taking advantage of such profitable substrate because of its abundance and easy acquisition.
This paper presents the results of an investigation aimed at understanding microstructure formati... more This paper presents the results of an investigation aimed at understanding microstructure formation of Al-Fe-Mn-Si intermetallics during pressure-assisted reactive sintering of elemental powders. The proportion of elements was selected such that the composition of the product was 55 wt % Al, 17 wt % Si, 14 wt % Mn, and 14 wt % Fe. Experiments were conducted at temperatures between 600 and 800°C, using compaction stresses of up to 20 MPa. Rietveld analysis of x-ray diffraction patterns of fully processed samples showed that the powders were transformed into a mixture of Al9FeMnSi and Al9FeMn2Si phases. However, as temperature and pressure were increased, the Al9FeMnSi phase was transformed into the Al9FeMn2Si phase. Differential Thermal Analysis, as well as microstructural characterization by scanning electron microscopy and x-ray diffraction, showed that these intermetallics do not form directly from the powder mixtures. Rather, they are the result of metallurgical reactions...
By using zeolite as an alternative substrate, in vitro germination of six cacti species was evalu... more By using zeolite as an alternative substrate, in vitro germination of six cacti species was evaluated. In vitro seeding was performed for: Astrophytum capricorne A. Dietr. Britton & Rose, A. myriostigma Lem., Echinocereus reichenbachii Terscheck ex Walp. Haage, Escobaria dasyacantha Engelm Britton & Rose, Mammillaria prolifera Mill Haw. and Sclerocactus scheeri Salm- Dyck N. P. Taylor. In order to do this, three particle sizes of zeolite were applied: thin (from 0.71 to 1 mm), medium (from 1.1 to 2 mm) and coarse (2.1 to 3.36 mm of calibration). A total of nine treatments were applied to zeolite's structures of the following granulometric sizes: fine, medium and coarse + distilled water (treatments 1, 2 and 3), three types of zeolites + Murashige and Skoog (MS) (treatment 4, 5 and 6) treatment 7 agar + MS + sucrose, treatment 8, agar + MS; and treatment 9 agar. The germination index evaluation results were statistically analyzed identifying highly significant differences for the...
Interrupted and continuous hot compression tests were performed for eutectoid steel over the temp... more Interrupted and continuous hot compression tests were performed for eutectoid steel over the temperature range of 850 to 1050 °C and while using strain rates of 0.001, 0.01, 0.1, and 1 s−1.The interrupted tests were carried out to characterize the kinetics of static recrystallization(SRX) and determinate the interpass time conditions that are required for initiation and propagation of dynamic recrystallization (DRX), while considering that the material does not contain microalloying elements additions for the recrystallization delay. Continuous testing was used to investigate the evolution of the austenite grain size that results from DRX. The results indicate that carbon content accelerates the SRX rate. This effect was observed when the retardation of recrystallization due to a decrease in deformation temperature from 1050 to 850 °C was only about one order of magnitude. The expected decelerate effect on the SRX rate when the initial grain size increases from 86 to 387 µm was not ...
ABSTRACTThis article outlines the use of quenching dilatometry in phase transformation kinetics r... more ABSTRACTThis article outlines the use of quenching dilatometry in phase transformation kinetics research in steels under continuous cooling conditions. For this purpose, the phase transformation behavior of a hot-rolled heat treatable steel was investigated over the cooling rate range of 0.1 to 200 °C/s. The start and finish points of the austenite transformation were identified from the dilatometric curves and then the continuous cooling transformation (CCT) diagrams were constructed. The experimental CCT diagrams were verified by microstructural characterization using scanning electron microscopy (SEM) and Vickers micro-hardness. In general, results revealed that the quenching dilatometry technique is a powerful tool for the characterization and study of solid-solid phase transformations in steels. For cooling rates between 200 and 25 °C/s the final microstructure consists on plate-like martensite with the highest hardness values. By contrast, a mixture of phases of ferrite, baini...
Another important application of aluminium scrap from cans is the production of automotive alloys... more Another important application of aluminium scrap from cans is the production of automotive alloys such as AA380, AA319 and AA356. However, these alloys specify no more than 0.10 wt.% Mg to avoid the harmful effects of Mg on mechanical properties, as shown by (Caseres, 1999). Various techniques have been developed to remove Mg from molten aluminium, such as methods based on gaseous mixtures of Ar/Cl 2 or Ar/SF 6. Other techniques are based on the optimisation of solid reactive groups like Na 2 SiF 6 , AlF 3 , KAlF 4 or SiO 2. Previous studies performed by (Martinez, 19998) on the removal of Mg from Al-Si-Cu alloys established that it is possible to remove Mg from 700 °C to 800 °C by injecting submerged SiO 2 powder. This author claims that Mg removal takes place through the formation of a complex MgAl 2 O 4 compound. On the other hand, (Escobedo et al., 2003) studied the removal of Mg from molten aluminium by injecting submerged powders of SiO 2 particles with an irregular morphology, determining the reaction rate and the values of some kinetic parameters of technological interest. For some initial conditions, it was possible to remove almost 100% of the Mg in time periods on the order of 70 min. The reaction was found to stop once the formation of a complex layer of reaction products covered the SiO 2 particles. These authors suggested that the predominant reaction is transitory, indicating that contact time between the molten phase and the solid particles is quite rapid, occurring in fractions of a second. Therefore, the main disadvantage of this process is the entrapment of solid particles in the solidified alloy, called inclusions, as well as the excessive formation of slag rich in MgAl 2 O 4 and agglomerates of Al 2 O 3-SiO 2 particles. To better understand the reactions involved in the injection of submerged powders of SiO 2 for Mg removal from molten aluminium, it is necessary to mention the elaboration of mullite refractories and metal-matrix composites. Al-Mg fibers surrounded by Al 2 O 3 SiO 2 are taken as the products of the reaction of MgO and MgAl 2 O 4. (Ghosh et al., 2003) studied the production of MgAl 2 O 4 by direct reaction between MgO and Al 2 O 3 at 1400 o C, represented by the next equation: MgO(s) + Al 2 O 3 (s) = MgAl 2 O 4 (s) (1) G°9 73K =-7,69 kcal/mol (Zhong et al., 1995) performed an extensive bibliographical investigation on interfacial reactions occurring during the production of aluminium-Al 2 O 3 fibers lined with SiO 2 composites, with several initial Mg concentrations. They analysed experiments performed by other authors, who found that MgAl 2 O 4 formed at the Al 2 O 3 fiber interface contained an Al alloy with 4 wt. % Mg, at 800 o C. (Fishkis, 1991) also confirmed the formation of MgAl 2 O 4 at the interface of Al 2 O 3 fibers lined with SiO 2 , embedded in an aluminium alloy containing 3 wt. % Mg. However, in similar experiments performed by (Pai & Ray, 1976) they found MgO as the main reaction product, although the alloys tested contained more than 4 wt.% Mg. The proposed reaction is: 3Mg (Al) + Al 2 O 3 (s) =3MgO(s) + 2Al(l) (2) G°9 73K =-28,63 kcal/mol (Pfeifer et al., 1990) found similar results to those reported by Pai et al. They accept the formation of MgO via the reaction given by equation (2), indicating that MgO could also be formed by direct reaction between dissolved Mg and O 2 from the atmosphere, according to: 286
In this paper it is shown that pneumatically injected gaseous mixtures containing SF6 (g) are use... more In this paper it is shown that pneumatically injected gaseous mixtures containing SF6 (g) are useful to oxidize the magnesium dissolved in molten aluminum alloys. Although the oxidation of magnesium with SF6 (g) is thermodynamically favorable, the addition of ...
In this work it is described an experimental procedure that led to the development of molten alum... more In this work it is described an experimental procedure that led to the development of molten aluminum protecting fluxes for its usage in reverberatory furnaces. Technical, ecological and economic aspects were taken into account. The composition of fluxes was based on the equimolar NaCl-KCl composition, using different fluorides to complete the formulation (NaF, KF, LiF, Na 3 AlF 6). The different fluxes were tested first at a laboratory scale. Furthermore, the one that showed the best performance regarding the efficiency of recovering of molten metal was tested at industrial trials level. From the laboratory scale test results, the best performance was observed for a formulation containing 90 wt. % NaCl-KCl, plus 10 wt. % Na 3 AlF 6. This formulation was tested at industrial level, reducing the melt losses from 9.46 % up to 5.87%. Previously, molten metal losses were evaluated for both laboratory and industrial tests without the use of covering fluxes.
This work reports the results of laboratory experiments conduced to follow the kinetics of stront... more This work reports the results of laboratory experiments conduced to follow the kinetics of strontium recovery into the Al-Mg alloy by metallothermic reduction of SrO. The reagent was incorporated to molten alloy by the use of submerged powders injection technique. The variables analyzed were the injection time, the melt temperature and the initial magnesium content. Magnesium is added to the melt to increase the reactivity and reduce the surface tension of the molten aluminum. It was possible to increase the strontium content from 0 to 5 wt.% after 60 min of treatment. The results were fitted to a general kinetic equation, which allowed it to obtain the kinetic parameters, i.e. order of reaction and activation energy of the process. As the main mechanism of the strontium recovery process is of diffusive type, the global process rate increases as the temperature and initial amount of the magnesium increased.
This work presented the feasibility of cerium recovery by Al-Mg alloy through the metallothermic ... more This work presented the feasibility of cerium recovery by Al-Mg alloy through the metallothermic reduction of CeO 2 to obtain a master alloy Al-4%Ce. The master alloy obtained in this investigation was for the grain refinement and modification of Al-Si alloys. The reagent was incorporated into a molten alloy using the submerged powder injection technique, and metallic samples were obtained during injection. Chemical and microstructural analyses (by inductively coupled plasma (ICP) and scanning electron microscopy (SEM), respectively) confirmed the possibility of Ce uptake in the bath (0 to 4 wt.%), as CeO 2 was reduced through metallothermic reactions in the molten alloys. Based on the characterization of reaction products, the sequence of the reaction was proposed.
Al respecto, Bunt (1988) señala que la calidad de las plántulas depende del tipo de sustrato dond... more Al respecto, Bunt (1988) señala que la calidad de las plántulas depende del tipo de sustrato donde se desarrollan, en particular de sus características físico-químicas, ya que el desarrollo y el funcionamiento de las raíces están MS treatment. The species with the highest germination response was E. dasyacantha (92.6%), followed by A. myriostigma (54.07%). This protocol calls for the convenience of using zeolites as a replacement for agar substrate, thus promoting the cacti in vitro conservation, taking advantage of such profitable substrate because of its abundance and easy acquisition.
This paper presents the results of an investigation aimed at understanding microstructure formati... more This paper presents the results of an investigation aimed at understanding microstructure formation of Al-Fe-Mn-Si intermetallics during pressure-assisted reactive sintering of elemental powders. The proportion of elements was selected such that the composition of the product was 55 wt % Al, 17 wt % Si, 14 wt % Mn, and 14 wt % Fe. Experiments were conducted at temperatures between 600 and 800°C, using compaction stresses of up to 20 MPa. Rietveld analysis of x-ray diffraction patterns of fully processed samples showed that the powders were transformed into a mixture of Al9FeMnSi and Al9FeMn2Si phases. However, as temperature and pressure were increased, the Al9FeMnSi phase was transformed into the Al9FeMn2Si phase. Differential Thermal Analysis, as well as microstructural characterization by scanning electron microscopy and x-ray diffraction, showed that these intermetallics do not form directly from the powder mixtures. Rather, they are the result of metallurgical reactions...
By using zeolite as an alternative substrate, in vitro germination of six cacti species was evalu... more By using zeolite as an alternative substrate, in vitro germination of six cacti species was evaluated. In vitro seeding was performed for: Astrophytum capricorne A. Dietr. Britton & Rose, A. myriostigma Lem., Echinocereus reichenbachii Terscheck ex Walp. Haage, Escobaria dasyacantha Engelm Britton & Rose, Mammillaria prolifera Mill Haw. and Sclerocactus scheeri Salm- Dyck N. P. Taylor. In order to do this, three particle sizes of zeolite were applied: thin (from 0.71 to 1 mm), medium (from 1.1 to 2 mm) and coarse (2.1 to 3.36 mm of calibration). A total of nine treatments were applied to zeolite's structures of the following granulometric sizes: fine, medium and coarse + distilled water (treatments 1, 2 and 3), three types of zeolites + Murashige and Skoog (MS) (treatment 4, 5 and 6) treatment 7 agar + MS + sucrose, treatment 8, agar + MS; and treatment 9 agar. The germination index evaluation results were statistically analyzed identifying highly significant differences for the...
Interrupted and continuous hot compression tests were performed for eutectoid steel over the temp... more Interrupted and continuous hot compression tests were performed for eutectoid steel over the temperature range of 850 to 1050 °C and while using strain rates of 0.001, 0.01, 0.1, and 1 s−1.The interrupted tests were carried out to characterize the kinetics of static recrystallization(SRX) and determinate the interpass time conditions that are required for initiation and propagation of dynamic recrystallization (DRX), while considering that the material does not contain microalloying elements additions for the recrystallization delay. Continuous testing was used to investigate the evolution of the austenite grain size that results from DRX. The results indicate that carbon content accelerates the SRX rate. This effect was observed when the retardation of recrystallization due to a decrease in deformation temperature from 1050 to 850 °C was only about one order of magnitude. The expected decelerate effect on the SRX rate when the initial grain size increases from 86 to 387 µm was not ...
ABSTRACTThis article outlines the use of quenching dilatometry in phase transformation kinetics r... more ABSTRACTThis article outlines the use of quenching dilatometry in phase transformation kinetics research in steels under continuous cooling conditions. For this purpose, the phase transformation behavior of a hot-rolled heat treatable steel was investigated over the cooling rate range of 0.1 to 200 °C/s. The start and finish points of the austenite transformation were identified from the dilatometric curves and then the continuous cooling transformation (CCT) diagrams were constructed. The experimental CCT diagrams were verified by microstructural characterization using scanning electron microscopy (SEM) and Vickers micro-hardness. In general, results revealed that the quenching dilatometry technique is a powerful tool for the characterization and study of solid-solid phase transformations in steels. For cooling rates between 200 and 25 °C/s the final microstructure consists on plate-like martensite with the highest hardness values. By contrast, a mixture of phases of ferrite, baini...
Another important application of aluminium scrap from cans is the production of automotive alloys... more Another important application of aluminium scrap from cans is the production of automotive alloys such as AA380, AA319 and AA356. However, these alloys specify no more than 0.10 wt.% Mg to avoid the harmful effects of Mg on mechanical properties, as shown by (Caseres, 1999). Various techniques have been developed to remove Mg from molten aluminium, such as methods based on gaseous mixtures of Ar/Cl 2 or Ar/SF 6. Other techniques are based on the optimisation of solid reactive groups like Na 2 SiF 6 , AlF 3 , KAlF 4 or SiO 2. Previous studies performed by (Martinez, 19998) on the removal of Mg from Al-Si-Cu alloys established that it is possible to remove Mg from 700 °C to 800 °C by injecting submerged SiO 2 powder. This author claims that Mg removal takes place through the formation of a complex MgAl 2 O 4 compound. On the other hand, (Escobedo et al., 2003) studied the removal of Mg from molten aluminium by injecting submerged powders of SiO 2 particles with an irregular morphology, determining the reaction rate and the values of some kinetic parameters of technological interest. For some initial conditions, it was possible to remove almost 100% of the Mg in time periods on the order of 70 min. The reaction was found to stop once the formation of a complex layer of reaction products covered the SiO 2 particles. These authors suggested that the predominant reaction is transitory, indicating that contact time between the molten phase and the solid particles is quite rapid, occurring in fractions of a second. Therefore, the main disadvantage of this process is the entrapment of solid particles in the solidified alloy, called inclusions, as well as the excessive formation of slag rich in MgAl 2 O 4 and agglomerates of Al 2 O 3-SiO 2 particles. To better understand the reactions involved in the injection of submerged powders of SiO 2 for Mg removal from molten aluminium, it is necessary to mention the elaboration of mullite refractories and metal-matrix composites. Al-Mg fibers surrounded by Al 2 O 3 SiO 2 are taken as the products of the reaction of MgO and MgAl 2 O 4. (Ghosh et al., 2003) studied the production of MgAl 2 O 4 by direct reaction between MgO and Al 2 O 3 at 1400 o C, represented by the next equation: MgO(s) + Al 2 O 3 (s) = MgAl 2 O 4 (s) (1) G°9 73K =-7,69 kcal/mol (Zhong et al., 1995) performed an extensive bibliographical investigation on interfacial reactions occurring during the production of aluminium-Al 2 O 3 fibers lined with SiO 2 composites, with several initial Mg concentrations. They analysed experiments performed by other authors, who found that MgAl 2 O 4 formed at the Al 2 O 3 fiber interface contained an Al alloy with 4 wt. % Mg, at 800 o C. (Fishkis, 1991) also confirmed the formation of MgAl 2 O 4 at the interface of Al 2 O 3 fibers lined with SiO 2 , embedded in an aluminium alloy containing 3 wt. % Mg. However, in similar experiments performed by (Pai & Ray, 1976) they found MgO as the main reaction product, although the alloys tested contained more than 4 wt.% Mg. The proposed reaction is: 3Mg (Al) + Al 2 O 3 (s) =3MgO(s) + 2Al(l) (2) G°9 73K =-28,63 kcal/mol (Pfeifer et al., 1990) found similar results to those reported by Pai et al. They accept the formation of MgO via the reaction given by equation (2), indicating that MgO could also be formed by direct reaction between dissolved Mg and O 2 from the atmosphere, according to: 286
In this paper it is shown that pneumatically injected gaseous mixtures containing SF6 (g) are use... more In this paper it is shown that pneumatically injected gaseous mixtures containing SF6 (g) are useful to oxidize the magnesium dissolved in molten aluminum alloys. Although the oxidation of magnesium with SF6 (g) is thermodynamically favorable, the addition of ...
In this work it is described an experimental procedure that led to the development of molten alum... more In this work it is described an experimental procedure that led to the development of molten aluminum protecting fluxes for its usage in reverberatory furnaces. Technical, ecological and economic aspects were taken into account. The composition of fluxes was based on the equimolar NaCl-KCl composition, using different fluorides to complete the formulation (NaF, KF, LiF, Na 3 AlF 6). The different fluxes were tested first at a laboratory scale. Furthermore, the one that showed the best performance regarding the efficiency of recovering of molten metal was tested at industrial trials level. From the laboratory scale test results, the best performance was observed for a formulation containing 90 wt. % NaCl-KCl, plus 10 wt. % Na 3 AlF 6. This formulation was tested at industrial level, reducing the melt losses from 9.46 % up to 5.87%. Previously, molten metal losses were evaluated for both laboratory and industrial tests without the use of covering fluxes.
Uploads
Papers by Alfredo Flores